1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling a vehicular air-conditioning system to control a fuel-combustion heater for producing combustion heat to heat a heating medium in a heating medium circuit which heats air flowing through a duct through a heat exchange between the heating medium and the air.
2. Description of the Related Art
Many air-conditioning principles are employed to air-condition the passenger compartment of a vehicle. One air-conditioning system is of the air reheating type which heats cool air that has been dehumidified by an evaporator by passing the cool air through a heater core, and discharges temperature-controlled air and humidity-controlled air from respective outlets into the passenger's compartment. According to an air-mixing-type design, cool air that has passed through an evaporator is divided by an air-mixing damper into air to pass through a heater core and air to bypass the heater core, and hot air and cool air are mixed downstream of the heater core and discharged through respective outlets into the passenger's compartment.
Air-conditioning systems for use on electric vehicles cannot use a heating medium in the form of cooling water which would otherwise be heated by cooling internal combustion engines. Japanese laid-open patent publication No. 8-197937 discloses an air-conditioning system which is capable of providing a sufficient heating capability and uses an existing heater unit, for use on an electric vehicle.
The disclosed air-conditioning system has a duct for passing air therethrough into a passenger's compartment, wherein the air-conditioning system operates selectively in a refrigerating cycle which involves an air blower for delivering air through the duct into the passenger's compartment, a coolant compressor for compressing and discharging a coolant, a coolant-water heat exchanger for heating hot water through heat exchange between the compressed coolant discharged from the coolant compressor and the hot water, and a coolant evaporator for cooling air with the heat of evaporation of the coolant, and in a hot-water cycle which involves a pump for circulating the hot water heated by the coolant-water heat exchanger and a hot-water heater disposed in the duct for heating air flowing through the duct with the hot water flowing from the coolant-water heat exchanger. The hot-water cycle also involves a fuel-combustion heater, connected in series with the hot-water heater, for heating the hot water with heat generated when a fuel is combusted, in order to obtain a sufficient heating capability in cold climates.
The fuel-combustion heater is basically controlled in three modes, i.e., an igniting mode, a combustion ability switching mode (mode of normal heating operation), and an extinguishing mode. Usually, the fuel-combustion heater switches from the igniting mode to the combustion ability switching mode to the extinguishing mode. If the passenger wants to turn off the fuel-combustion heater while it is operating in the combustion ability switching mode, then the passenger presses an "OFF" switch or an "AUX HTR OFF" switch on the air-conditioner control panel to cause the fuel-combustion heater to enter the extinguishing mode for thereby switching off the fuel-combustion heater.
Even if the passenger presses the "OFF" switch or the "AUX HTR OFF" switch by mistake, the fuel-combustion heater switches from the combustion ability switching mode to the extinguishing mode, and is turned off. Therefore, when the passenger presses an "AUTO" switch on the air-conditioner control panel to start heating the hot water with the fuel-combustion heater, it takes a considerable period of time until the fuel-combustion heater switches from the igniting mode to the combustion ability switching mode. Before the fuel-combustion heater operates in the combustion ability switching mode, the temperature in the passenger compartment drops to such a level that the passenger will feel too cold in the passenger compartment.